1. Field of the Invention
The present invention relates to an imaging apparatus, a radiation imaging system, and a controlling method of the imaging apparatus suitably used for medical diagnosis or industrial non-destructive tests. The term “radiation” herein includes x-rays, electromagnetic waves such as γ-rays, and particulate beams such as α-rays and β-rays.
2. Description of the Related Art
In recent years, a radiation imaging apparatus using a flat radiation detection portion (or Flat Panel Detector, hereinafter referred to as a “FPD”) made of semiconductor material has been in practical use as an imaging apparatus used for medical image diagnosis or non-destructive tests with x-rays. The radiation imaging apparatus using the FPD is capable of digital photographing, and can convert radiation such as x-rays that has passed through a subject such as a patient into an analog electric signal with the FPD and perform analog/digital conversion of the analog electric signal to obtain a digital image signal. FPDs are mainly classified into a direct conversion type FPD and an indirect conversion type FPD. The direct conversion type radiation imaging apparatus includes FPDs that has a plurality of pixels arranged two-dimensionally, where each of the pixels includes a conversion element made of semiconductor material such as a-Se that can directly convert radiation into an electric charge. The indirect conversion type radiation imaging apparatus includes FPDs that have a plurality of pixels arranged two-dimensionally, where each of the pixels includes a conversion element having a wavelength converter such as a fluorescent material that can convert radiation into light and a photoelectric conversion element made of semiconductor material such as a-Si that can convert light into electric charges. An indirect conversion type radiation imaging apparatus is disclosed, for example, in U.S. Patent Application Publication No. 2002/0050940. The radiation imaging apparatus including the FPD can convert a radiation image into digital information, and can practically instantaneously transmit image information over a distance. The radiation imaging apparatus including such an FPD is used as a digital imaging apparatus for general photography to obtain a still image and fluoroscopy to obtain a moving image, for example, in medical image diagnosis. U.S. Patent Application Publication No. 2002/0050940 discloses an imaging apparatus using a signal processing apparatus that can read out an image signal from a converting portion at high speed without reducing the S/N ratio, the converting portion including pixels arranged in a matrix, where each of the pixels includes a conversion element.
A converting portion of an imaging apparatus disclosed in U.S. Patent Application Publication No. 2002/0050940 includes a plurality of pixels arranged in a matrix, where each of the pixels includes a conversion element converting radiation or light into electric charges and an output switch element performing an output operation of outputting an electric signal based on the electric charges. A plurality of drive wires is arranged in a column direction, and each of the drive wires is commonly connected to the plurality of pixels in a row direction. An outputting drive circuit is connected to the drive wires, and applies row by row a drive signal for controlling the output operation to the pixels through the drive wires. Thus, the outputting drive circuit controls the converting portion so as to perform the output operation row by row. Further, the converting portion outputs row by row the electric signals from the pixels in parallel, and thus a plurality of signal wires for transmitting the electric signal is arranged in the row direction, and each of the signal wires is commonly connected to output terminals of the output switch elements of the plurality of pixels in the column direction. The signal wires of the converting portion are connected to a read-out circuit, and the read-out circuit reads out the electric signal output from the pixel in the converting portion through the signal wire in parallel, converts the signal into a serial electric signal, and outputs the serial electric signal.
When the electric signal from the converting portion is read out by the read-out circuit in such an imaging apparatus, the below described operations are performed. First, a predetermined constant potential is provided to the signal wire and the read-out circuit to reset a transmitting path (here, the signal wire). An operation for resetting the transmitting path such as the signal wire is referred to as a reset operation. Then, a drive signal is provided to a drive wire in a first row, and an output switch element in the first row performs the output operation to output an electric signal from a pixel in the first row to the signal wire. The electric signal output to the signal wire is sampled and temporarily held by a temporary storage unit such as a sampling and holding circuit provided for each signal wire in the read-out circuit. This operation is referred to as a sampling and holding operation. After the electric signal is held by the sampling and holding circuit, the transmitting path is again reset to be ready for an output operation in the next row. Then, a drive signal is provided to a drive wire in a second row, and an output switch element in the second row performs an output operation to output an electric signal from a pixel in the second row to a signal wire. As such, the reset operation, the output operation, and the sampling and holding operation are performed row by row, and image signals for one image are read out from the converting portion to the read-out circuit. The operation of reading out the image signals for one image from the converting portion to the read-out circuit is referred to as a “read-out operation”.
In such an imaging apparatus, the drive wire and the signal wire in the converting portion are arranged with an intersection. Thus, a potential change component due to a potential change of a leading edge or a trailing edge of a drive signal applied to the drive wire is mixed into an electric signal transmitted through the signal wire via a capacitance at the intersection. Further, when a transistor having a control terminal (gate) and two main terminals (source and drain) as output switch elements is used, a potential change component is mixed into an electric signal transmitted via a capacitance between gate and source (Cgs). In U.S. Patent Application Publication No. 2002/0050940, the output operation is performed between the reset operation and the sampling and holding operation in the transmitting path such as the signal wire. Thus, the potential change component due to the leading edge of the drive signal is canceled by the potential change component due to the trailing edge of the drive signal, and the potential change does not influence the output and held electric signal.